1. Field of the Invention
The present invention relates in general to a brake booster which permits the driver to easily brake the vehicle by exerting only a little pressure on the brake pedal, and more particularly to a pneumatic brake booster which is equipped with a pressure control means by which the pressure supplied to the work chamber of the booster is suitably controlled in accordance with a force practically applied to the brake pedal by the driver. More specifically, the present invention is concerned with a pneumatic brake booster which holds therein a pressure sensor for detecting the force practically applied to an input rod of the booster from the brake pedal.
2. Description of a Prior Art
Hitherto, various kinds of brake boosters have been proposed and put into practical use in a field of automotive brakes. Some of them are of a pneumatic type using a pressurized air as medium for actuating a power piston in the booster. Japanese Patent First Provisional Publication No. 58-188746 proposes to incorporate the boosters of such type with an electronic pressure control means by which the pressure applied to the work chamber of the booster is electronically controlled in accordance with a force practically applied to the brake pedal by the driver. In this regard, the Publication discloses a brake booster equipped with a pressure sensor which detects the brake pedal force practically applied to an input rod of the booster from the brake pedal. Since the output characteristic of the booster can be easily changed by only adjusting the control means, such boosters are widely applicable to various types of motor vehicle. However, due to their inherent constructions, it sometimes occurs that a great pressure above 900 Kg is directly applied to the pressure sensor proper during braking of the vehicle, particularly, upon sudden braking. Thus, the pressure sensors used in such boosters must have steady and strong constructions in order to avoid breakage thereof. However, as is known, such construction brings about increased cost of productions.